Table 6. Internal Inch Screw Thread Calculations for 19 ∕ Table 6. (Continued) Internal Inch Screw Thread Calculations for 19 ∕
64 -28 UNS-2B
64 -28 UNS-2B
Characteristic Description
Calculation
Notes
Maximum internal pitch diameter ( D 2 max ) = minimum internal pitch diameter ( D 2 min ) + internal pitch diameter tolerance (TD 2 )
D D TD max min 2 2 2 = +
TD 2 = external pitch diameter tolerance
The constant 1.30 is for this Class 2B example, and will be different for Classes 1B and 3B. Td 2 for Class 2A (see calculation, Table 5) is rounded to six decimal places D 2 max is rounded to four decimal places
. 130 2 1 30 0 003127 0 0040651 0 0041 for Class . . . . Td A 2 # # = = ^ h
TD
= =
2
External pitch diameter tolerance TD 2
. . D D TD 0 2789 0 0041 0 2830 max min 2 2 2 = + = + = .
Maximum internal pitch diameter ( D 2 max ) Minimum internal major diameter ( D min ) = basic major diameter ( D bsc )
. 02969 D D min D min is rounded to four decimal places Table 7. Number of Decimal Places for Intermediate and Final Calculations of Thread Characteristics bsc = =
Final
Intermediate
Final
Symbol
Dimensions
Inch Metric
Symbol
Dimensions
Inch Metric Inch Metric 6 N/A … … … … 8 Note a
Major diameter, external thread Major diameter, internal thread Pitch diameter, external thread Pitch diameter, internal thread Minor diameter, external thread
4 4 4 4 4 4
3 3 3 3 3 3
Length of thread engagement
d
LE
Pitch
D d 2
P
Major diameter tolerance
… … 4 … … 6 … … 4 … … 4
3 3 3 3
Td
Pitch diameter tolerance, external thread Pitch diameter tolerance, internal thread Minor diameter tolerance, internal thread
D 2 d 1 d 3 D 1
Td 2 TD 2 TD 1
Minor diameter, rounded root external thread Minor diameter, internal threads for sizes 0.138 and larger for Classes 1B and 2B only Minor diameter, internal threads for sizes smaller than 0.138 for Classes 1B and 2B, and all sizes for Class 3B
h b = 2 h as Twice the external thread addendum
6 N/A … …
3 N/A
Double height of UNR external thread
6 N/A … …
4 N/A 2 h s
D 1
Minor diameter, internal metric thread
N/A 3
2 h n
Double height of internal thread and UN external thread
6 N/A … …
D 1
Allowance at major pitch and minor diameters of external thread
es 6 N/A … … a Metric pitches are not calculated. They are stated in the screw thread designation and are to be used out to the number of decimal places as stated. Note: Constants based on a function of P are rounded to an 8-place decimal for inch threads and a 7-place decimal for metric threads. 3 Twice the external thread addendum
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